During a trip to Senegal, Maya Angelou called Samia, a friend she had made in Paris several years before, and was invited over for dinner. Passing a room where people apparently clung to the wall to avoid standing on the rug, Angelou became incensed. "I had known a woman in Egypt who would not allow her servants to walk on her rugs, saying that only she, her family and friends were going to wear out her expensive carpets. Samia plummeted in my estimation."

Keen to challenge her host's hauteur, she walked back and forth across the carpet. "The guests who were bunched up on the sidelines smiled at me weakly." Soon afterwards, servants came, rolled up the rug, took it away and brought in a fresh one. Samia then came in and announced that they would be serving one of Senegal's most popular dishes in honour of Angelou: "Yassah, for our sister from America… Shall we sit?" And as the guests went to the floor where glasses, plates, cutlery and napkins were laid out on the carpet, Angelou realised the full extent of her faux pas and was "on fire with shame".

"Clever and so proper Maya Angelou, I had walked up and down over the tablecloth… In an unfamiliar culture, it is wise to offer no innovations, no suggestions, or lessons. The epitome of sophistication is utter simplicity." Such is an example of the 28 short epistles that comprise Letter To My Daughter, Angelou's latest book.

Elsewhere, she is beaten up by a lover, shaved by her mother before giving birth, nixes an offer to televise one of her stories because a producer is sniffy, and drinks coffee with cockroaches in it rather than insult her hosts, vomiting when she is out of sight.

Most end with the kind of wisdom that, depending on your taste, qualifies as either homespun or hokey. "I am never proud to participate in violence, yet I know that each of us must care enough for ourselves that we can be ready and able to come to our own defence when and wherever needed." Or, "All great artists draw from the same resource: the human heart, which tells us that we are all more alike than we are unalike."

At moments in the book she sounds like an elderly relative, distraught at the wayward manners of the young. In one, she delivers a broadside against vulgarity. "I'm always disappointed when people don't live up to their potential," she says to me. "I know that a number of people look down on themselves and consequently on everybody who looks like them." She suggests that this mindset is at the root of black kids thinking that to do well at school is to "act white". "But that, too, can change," argues Angelou, as she shifts into full-on aspirational gear. "I like the idea that people can have a dress-up night. I like the idea that people might have a tuxedo or a cocktail dress. It means 'I have a place to go.' It means, 'I can be better than this. I can speak more intelligently than this. I can cook more deliciously.' "

At other times she sounds like the kind of elderly relative who has outlived the need for social convention. Arguing for honesty at every level of human contact, she writes: "When people ask, 'How are you?' have the nerve sometimes to answer truthfully. You must know, however, that people will start avoiding you…" Sure enough, halfway through the interview she tells me I'm fat and suggests I pay more attention to the size of my portions. "You are going to have to lose that weight. You're too young and too handsome. Don't do it to yourself."

Given the exhaustive autobiographical work for which she is known, it is stunning to think that she has much more to share. She has written six memoirs, starting with her birth in St Louis, Missouri and ending with the assassination of Martin Luther King, whom she knew, which inspired her to write her first autobiographical work – I Know Why The Caged Bird Sings.

What prompted her to write this book? "I had no daughters," she says. "I had a son who was the best thing that ever happened to me in my life. But in reality I have lots of daughters. Black ones, white ones, Asian ones and Jewish ones and the Spanish-speaking ones… Sometimes I'll get a thousand pieces of mail a week from young women who think I'm wise. So they use me as a mother and I think of them as my daughters. So I thought it was time to say, 'Listen, kids, I have been here and done this. I got into this scrape and got out of it. I paid for it. I want you to know that if you take this road in the dark, to the left there's a big hole and if you're not careful you'll step in it and break your foot.' "

Most people would struggle to get one book out of their first 40 years. But then Angelou is not most people. She fell in plenty of holes, but somehow managed to come out skipping with her bones intact. To know her life story is to simultaneously wonder what on earth you have been doing with your own life and feel glad that you didn't have to go through half the things she has. Before she hit 40 she had been a professional dancer, prostitute, madam, lecturer, activist, singer and editor. She had lived in Ghana and Egypt, toured Europe with a dance troupe and settled in pretty much every region of the United States. She was raped as a child and did not speak for five years after the man who raped her was kicked to death – she believed that by saying who had done it, her voice itself had killed him. As a teenager her first sexual encounter – embarked upon because she was bored and insecure – produced a son, Guy. For the last 41 years she has hardly been idle. There have been several volumes of poetry, one of which – Just Give Me A Cool Drink Of Water 'Fore I Diiie – was nominated for a Pulitzer. She played Kunta Kinte's grandmother in Roots and wrote a screenplay, Georgia, Georgia, which was the first original script by a black woman to be produced. She recited her poem, On The Pulse Of The Morning, at Bill Clinton's inauguration and was one of the few women allowed to the podium to address Louis Farrakhan's Million Man March. She married at least three times.

For the last couple of decades she has merged her various talents into a kind of performance art – issuing a message of personal and social uplift by blending poetry, song and conversation.

She is like the Desiderata in human form – issuing a litany of imperatives and exhortations to be fabulous, conscious, passionate and compassionate. A professional hopemonger, her poems have titles such as Phenomenal Woman, Still I Rise and Weekend Glory. In the introduction to her latest book, she commands: "Try to be a rainbow in someone's cloud. Do not complain… Never whine… Be certain that you do not die without having done something wonderful for humanity."

I have met Angelou before, in 2002 in Los Angeles where she was performing. It was a great day. We had lunch and drank whiskey in her chauffeur-driven limo on the way to Pasadena where she was performing. En route I told her stories I hoped would make her laugh and she sang poetry. On the way back we drank more whiskey and she teased me about the pretentious hotel I was staying in.

Much about her remains the same. Her southern formality – addressing everybody by their surname and insisting on being addressed herself as Dr Angelou – remains, along with her cinnamon skin and an Olympian smile. She is still curious and extremely courteous. After asking after my family, she proceeds to ask the photographer's assistants their names and home towns, only to question them about the lineage of both and then offer a short history lesson. One of the assistant's names is Esner.

"That's German, isn't it?" she asks.

"I have no idea," he says.

"Yes, it was originally Eisner and they changed it."

And then there is the slow manner in which she speaks, not with a drawl, but deliberation. Rather than fly, she still prefers to ride on a tour bus. Back then she was renting Prince's bus while waiting for the one she designed to be decked out in kente cloth. Now she has another bus, which she also designed, covered in a different African print, in which she is planning to take the 42-hour drive from New York to San Francisco a few days after our interview.

When we first met she was in the process of buying property in Harlem. Now she is in it – a lordly brownstone, custom-built, complete with a lift, in the bosom of the area that produced so many of the poets she is keen on reciting. On the first floor the walls are decked with paintings, including several jazz trumpeters and a watercolour of Rosa Parks sitting at the front of the bus, alongside a Faith Ringgold work entitled Maya's Quilt Of Life and several African wall hangings.

But the biggest difference between then and now is her health. Seven years ago, when the subject of her age came up, she joked that her breasts were in a race to see which would touch her waist first and started singing the final verse of her poem On Aging:

"I'm the same person I was back then

A little less hair, a little less chin,

A lot less lungs and much less wind.

But ain't I lucky I can still breathe in."

I had observed: "She may pause to catch her breath mid-sentence. And her 6ft frame may move hesitantly and with a stoop. But beyond the inconveniences of time and gravity, she is in fine form."

Seven years on she is frail. Well enough to make it down the stairs on her own, but sufficiently delicate that she would measure each step as she measures her words – with care and caution. Then she needed only a cane and the occasional offer of an arm; today she uses a walker. At one point she gets frustrated when she tries to dial a number and her fingers refuse to comply. A plastic tube attached to her nose plies her with oxygen to help with her chronic obstructive pulmonary disease. One of her lungs has collapsed. "I smoked for 40 years, so I'm paying those dues," she says. Of the tube she says, "I sleep with it. I teach without it. I wouldn't go all day without it." And then she smiles. "But I'm fine as wine in the summertime."

Last month the TMZ website, which broke the news of Michael Jackson's passing, claimed she had been hospitalised in Los Angeles. By the time the blogosphere got hold of it there were rumours that she had died. The "news" reached CNN before one of Angelou's team pointed out that she was actually in St Louis, alive and well.

Angelou heard of her own death in the early hours of the morning and, not surprisingly, found the whole episode very upsetting: "My little grandson, the younger of the two, telephoned, and weeping, [said] 'I want to talk to my Grandma! Grandma! Grandma!' I said, 'I'm fine, honey,' " she later said.

"I have family in Europe and in Africa, and they have phoned me in tears, trying to find [out] am I all right, am I alive," Angelou told a local St Louis TV station. "I have family here, a family of friends here, all over the country, who called me, responding to an erroneous account that I was sick and maybe even dying in Los Angeles. I was anxious to come [back] to St Louis, but I wasn't dying even to come to St Louis," Angelou joked.

Nonetheless I suggest to her that there are moments in Letter To My Daughter that read like an extended farewell. In the space of the 500-word introduction, she mentions death twice and states near the beginning: "My life has been long, and believing that life loves the liver of it, I have dared to try many things, sometimes trembling, but daring still."

Angelou shrugs at the suggestion.

"Well I'm dealing with my 81-itis," she says, mildly whipping her oxygen cord for effect. "And I expect that next year it will be 82-itis. I don't have as far to go as I had to come. But I'm not making any arrangements and I plan to keep working as long as I can."

She is writing another cookbook, Great Food All Day Long, and when that is done she says she wants to write a letter to her sons.

I wonder what she will tell her sons about the presidential election of 2008. The year America elected a black man to be president and Angelou – who worked with both Malcolm X and Martin Luther King – backed his opponent, Hillary Clinton, in the Democratic primaries. Given her support for Clarence Thomas for the Supreme Court and her excitement at the appointment of Condoleezza Rice and Colin Powell to the Bush Administration, her support for Obama would have been consistent with a desire to see black faces in the highest places that is not obviously fettered by ideology. But Angelou, who was raised for much of her childhood in Stamps, Arkansas, had known Hillary for several decades and had liked what she had seen.

"My connection was with Hillary Clinton," she says. "I had watched her when she was the first lady of Arkansas. I thought this white girl would come to Arkansas and play croquet on the lawn and throw tea parties. And she was just the opposite. She worked on public health and education… even prisons. When her husband ran for the presidency and she said she was not going to bake cookies, I thought, 'I'm going to watch her for a while.'

"I told her then: 'If you ever run for anything, I've got your back. I'd never heard of Senator Obama. So when she said she was running for president I said, 'I've got your back.' "

When it became clear that Hillary could not win, some Democratic party grandees asked her to try to persuade Hillary to step down. "I told them, 'I'm backing her. I'll step down when she steps down.' When she stepped down, I went over to President Obama."

She concedes that she never thought America would put a black man in the White House in her lifetime. "In 100 years' time or maybe 50," she says. "But not now, no. I did not believe it could happen now."

With hindsight, how does she think it came about? "The terrorist action of 9/11 gave birth to President Obama's entry to the White House," she suggests. "Not directly but indirectly." She launches into a lyrical riff on Obama's campaign slogan, "Yes we can" which explains that that feeling of boundless possibility encompasses the best and worst of what the country has to offer.

"Yes I can. I can do whatever I want to do. I can do both the best and worst I can imagine. I can own human beings. I can have slaves. Yes I can. I can be the best human being ever. I can defeat slavery and segregation. Yes I can. I can be so cruel I can tax people out of their homes. Yes I can. I can have the greatest charities in the world. Yes I can."

The Bush Administration instilled, incited and then exploited fear, she says, which ran counter to the American spirit. "What happened was the leaders began to offer and introduce fear to the people. Fear?" she says, as though it were an aberration to America's national mood. "Braggadocio, yes. Boldness, yes. But get tin foil and scotch tape for your windows? It's ridiculous. It began to weaken the resolve that is American. So when someone said we are better than that, people breathed more freely. They wanted to say, Let America be America Again," she says, citing Langston Hughes's poem.

And what does she think now she has seen Obama in action? "Well, he's stepped into a hornets' nest," she says, referring to the mess Bush has bequeathed. "People want to know how he is doing during his first 100 days, but that's not realistic. We'll have to wait maybe two years."

Somehow, notwithstanding her support for Hillary, I had expected her to be more excited. But then I realise Obama is literally old enough to be her grandson and that she is not easily fazed. When I ask what she does to relax, it sounds as though she mostly naps, only to wake and receive awards. The night before our interview, she was being honoured with a $500-a-head fundraiser for the Maya Angelou Centre for Health Equity at Saks Fifth Avenue. The evening after, Black Entertainment Television was giving her the Healing The Race award. Two days later, she was honoured at Glamour magazine's 2009 women of the year, alongside Michelle Obama, Rihanna, Serena Williams and others. I joke that it was considerate of those who dispense awards to give her one day off. A smile stretches clean across her face.

"Well, it's Sunday," she says. "And I have to go to church." •

• Letter To My Daughter is published by Virago at £12.99. To order a copy for £11.99, including UK mainland p&p, go to guardian.co.uk/bookshop or call 0330 333 6846.